The changes in vascular functions and related physiological factors such as pO2 and pH in experimental tumors and normal tissues by X-irradiation and heat, and the role of such changes in the treatment of tumors by radiotherapy and hyperthermia alone or in combination will be investigated. The SCK tumors of A/J mice and RIF-1 tumors of C3H mice will be used as tumor model and the skin muscle of C3H mice and SD rats will be used as normal tissue model. Blood flow and blood volume will be measured with radioactive microspheres and radioactive RBC, respectively. The temperature profiles in tumors and normal tissues during heating, which is directly influenced by the heat dissipation by blood perfusion, will be monitored. The changes in oxygenation status, as a result of vascular changes, in tumors and normal tissues will be assessed by measuring pO2 with microelectrode. The changes in hypoxic cell fraction in tumors will also be measured and correlation between the change in pO2 and hypoxic cell fraction will be anaylzed. The implication of changes in oxygenation status of tumors and normal tissues in sequencing radiotherapy and hyperthermia will be critically assessed. The changes in acidity in the tissues will be determined by measuring pH with microelectrode and by biochemical determination of acidic metabolities such as lactic acid and B-hydroxybutric acid. The potential difference in the development of thermotolerance in tumors and normal tissues due to difference in pH and other microenvironmental factors will be analyzed. The information to be obtained in this study should help clinicians devise optimal treatment protocol of radiotherapy and hyperthermia used alone or in combination.